SARS is shown to have a recombinant ancestry comprised of a backbone from a Chinese/South East Asian lineage bat virus, and the Receptor Binding Domain (RBD) from a virus of African or European lineage. Aside from the geographical hurdle of such a union occurring naturally, the RBD incorporates additional substitutions and insertions that appear designed to enhance binding affinity non-specifically, disproportionately favoring residues that form strong hydrogen bonds and salt bridges. Few of these are conserved in related bat coronaviruses and there are additional indications that they may have been introduced artificially.